This invention relates to Cardiac ablation systems, and more particularly to a cardiac ablation system having a filter for filtering the ablation energy signal from intracardiac electrocardiogram wave forms.
One of the leading causes of death in the United States is cardiac arrhythmias, which are very rapid ineffectual contractions of the heart muscle. The most numerous cardiac arrhythmias are ventricular tachycardias (VT's) and supraventricular tachycardias (SVT's). SVT's originate in the left or right ventricle and are typically caused by arrhythmogenic sites associated with a prior myocardial infarction. SVT's originate in the atria and are typically caused by an accessory pathway. The presence of arrhythmogenic sites or accessory pathways located close to the inner surface of one of the heart chambers, can bypass or short circuit the normal electrical pathways potentially resulting in cardiac arrhythmia.
One method of treating tachycardias involves mapping the electrical activation sequence of the heart to locate the arrhythmogenic sites or accessory pathways and then to ablate the site by the application of a destructive energy source to the target tissue. Typical energy sources used for this purpose include direct current electrical energy, radio frequency electrical energy, laser energy and the like.
During the ablation process, the patient is monitored by acquiring ECG data from body surface electrocardiographs and intracardiac electrocardiograms while the patient's heart is paced by an external source. The amplitude of the electrogram wave forms derived from the electrodes placed in the heart are typically several orders of magnitude lower than the energy levels applied to the same catheter by the ablation generator. As a result, the application of radio frequency ablation energy interferes with at least some of the intracardiac electrocardiogram wave forms. Such interference produced by the application of ablation energy masks the underlying electrocardiogram wave form thereby negating the ability of the physician to monitor the electrocardiogram derived from the catheter electrodes through which ablation energy is applied.